. Bulletin. Forests and forestry -- United States. 48 TIMBER. 4. Soft woods requiring less than 1,600 pounds per square inch to produce an indentation of one-twentieth inch: The greater mass of coniferous wood; pine, spruce, fir, hemlock, cedar, cypress, and red- wood; poplar, tulip, basswood, butternut, chestnut, buckeye, and catalpa. CLEAVABILITY. When an ax is struck into a piece of wood as shown in fig. 33 the cleft projects beyond the blade of the ax and the process is not one of cutting, but of tension across the grain. The ax presses on a lever, a b, while the surface in which the trans
. Bulletin. Forests and forestry -- United States. 48 TIMBER. 4. Soft woods requiring less than 1,600 pounds per square inch to produce an indentation of one-twentieth inch: The greater mass of coniferous wood; pine, spruce, fir, hemlock, cedar, cypress, and red- wood; poplar, tulip, basswood, butternut, chestnut, buckeye, and catalpa. CLEAVABILITY. When an ax is struck into a piece of wood as shown in fig. 33 the cleft projects beyond the blade of the ax and the process is not one of cutting, but of tension across the grain. The ax presses on a lever, a b, while the surface in which the transverse tension takes place is reduced almost to a line across the stick at b. If the wood is very elastic, the cleft runs far ahead of the ax, the lever arm a b is long, and the resistance to splitting proportionately small. Elasticity, therefore, helps splitting, while great shearing strength, a good measure for transverse tension and hardness hinder it. Wood splits naturally along two normal planes, the most readily along the radius, because the arrangement of fibers and pith rays is radial, and next along the tangent, or with the annual rings, because the softer spring wood forms continuous planes in this direction. Cleavage along the radius, however, is from 50 to 100 x>er cent easier, and only in case of cross grain, etc., the cleavage along the ring becomes the easier. In the wood of conifers, wood fibers and pith rays are very reg- ular, the former in perfect radial series or rows, and cleavage is, therefore, very easy in this direc- tion. The same is brought about in the oak by the very high pith rays, but where they are thick and low, as in sycamore, and generally in the butt cuts and about knots, they impede cleavage by causing a greater irregularity in the course of the wood fibers. The greater the contrast of spring and summer wood, the easier the cleav- age tangentially or in the direction of the rings. This is especially marked in conifers and also in woods like
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